This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-100231, filed Apr. 7, 1999; and No. 2000-069689, filed Mar. 14, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a mobile communication terminal apparatus, a hand-over control device, a hand-over controlling method and a storage medium storing the hand-over controlling method, which are used in a cellular mobile communication system, and more particularly to a mobile communication terminal apparatus having a function of detecting the quality degradation of a radio channel and requesting a base station to operate the hand-over, a hand-over control device, a hand-over controlling method and a storage medium storing the hand-over controlling method.
Recently, a cellular mobile communication system whose typical is a portable telephone system, has been rapidly spread. The cellular mobile communication system distributes a plurality of base stations in a service area and forms a radio zone called a cell by these base stations. Then, the system connects a mobile communication terminal apparatus to the base stations of the radio zone where the terminal apparatus exists via a radio channel and further connects this base station to a terminal apparatus of a communication partner via a public network or the like, and thereby implements the communication between the terminals.
Incidentally, when the mobile terminal apparatus moves from a radio zone where it currently exists to another radio zone during the standby time or communication time, changing the base station in the established synchronization to the base station of the moving destination or what is called hand-over occurs in this type of the system. The hand-over operations will be explained below by exemplifying a system adopting the CDMA (Code Division Multiple Access) system.
That is, the CDMA mobile communication terminal apparatus measures the receipt level of a pilot signal transmitted by the base station in the established synchronization and also measures each of receipt levels of pilot signals transmitted by respective neighboring base stations, during the standby time or communication time. As for the strength of the receipt level, a ratio (Ec/Io) of the energy (Ec) of the despread pilot signal from the base station which is to be measured to the total receipt energies (Io) of the despread pilot signals may be used. When the receipt level from a neighboring base station is equal to or higher than a predetermined level in terms of the strength, or when the ratio of the receipt level from the base station which is in the established synchronization to the receipt level from the neighboring base station exceeds a predetermined value, the apparatus generates a message for requesting the hand-over and transmits it to the base station in the established synchronization. At this time, the measurement value of the receipt level from the base station in the established synchronization and the measurement values of the receipt levels from the neighboring base stations, are inserted into the message for requesting the hand-over.
When the base station receives the message for requesting the hand-over from the mobile communication terminal apparatus, a base station at the hand-over destination is determined on the basis of the measurement values of the receipt levels from the base stations that are inserted into the message, and this determined hand-over destination is noticed to the mobile communication terminal apparatus that has requested the hand-over. When the mobile communication terminal apparatus receives this notice, the apparatus makes a response to the base station and then changes the base station in the established synchronization on the basis of the notice. Thus, the hand-over of the mobile communication terminal apparatus is executed.
However, this kind of the conventional system has the following problem that should be solved. When the mobile communication terminal apparatus transmits the message for requesting the hand-over, the apparatus waits for a response message representing the acknowledgement that is to be sent back from the base station. If the response message representing the acknowledgement has not been sent back within a certain time, the apparatus assumes that the quality of the radio channel is temporarily degraded, and then repeats the transmission of the message for requesting the hand-over in a predetermined access sequence at the times designated by the base station.
However, if the measurement value of the receipt level is not noticed to the base station by the repeated transmissions, the noticed measurement value of the receipt level is often different from an actual measurement value at the current time. Particularly, if the mobile communication terminal apparatus moves at a high speed, the difference between the noticed measurement value and the actual value becomes larger since a point where he receipt levels from the respective base stations are measured largely changes to the position of the mobile communication terminal apparatus at the time when the hand-over requesting message actually reaches the base station. In such a case, the base station determines the hand-over destination on the basis of the previous measurement value that is different from the actual one and, therefore, the hand-over may not be properly executed.
The present invention is accomplished in consideration of the above circumstances, and its object is to provide a mobile communication terminal apparatus capable of allowing the hand-over to be executed to an optimum base station at any time even when the request for the hand-over is noticed by the repeated transmissions of the message, and thereby keeping the stable communication.
In according to one aspect of the present invention, there is provided a mobile communication terminal apparatus having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to a base station in a state of being in the established synchronization with any one of a plurality of base stations. The mobile communication terminal apparatus is characterized by comprising: hand-over determination means for measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; message transmission means for generating a request message including the measured qualities and transmitting the generated request message to the synchronized base station when it is determined by the hand-over determination means that the hand-over is necessary; message retransmission means for monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message and repeating the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and receiving quality update means for renewing the measured qualities included in the message to latest values before the message retransmission means retransmits the request message.
Therefore, according to this invention, when the request message is retransmitted, the receiving quality measurement values inserted into the message are always updated to the latest values. For this reason, the destination of the hand-over can be always determined on the basis of the latest measurement values and thereby the optimum hand-over can be always executed, at the base station.
In according to the other aspect of the present invention, there is provided a mobile communication terminal apparatus having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to a base station in a state of being in the established synchronization with any one of a plurality of base stations. The mobile communication terminal apparatus is characterized by comprising: hand-over determination means for measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; message transmission means for generating a request message including the measured qualities and transmitting the generated request message to the synchronized base station when it is determined by the hand-over determination means that the hand-over is necessary; message retransmission means for monitoring an response of acknowledgement from the base station to the transmission of the request message, and repeating the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and receiving quality update means for re-measuring the receiving qualities of the radio signals transmitted by the base station in the established synchronization and the neighboring base stations, after it is detected that there is no response of acknowledgement from the base station, and renewing the measured qualities included in the message to latest values on a basis of a result of the re-measurement.
With this structure, in the request message that is to be retransmitted, the receiving quality measurement values measured after the necessity of the retransmission is determined are inserted. For this reason, the latest receiving quality measurement values can be always noticed to the base station.
In according to the other aspect of the present invention, there is provided a mobile communication terminal apparatus having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to a base station in a state of being in the established synchronization with any one of a plurality of base stations. The mobile communication terminal apparatus is characterized by comprising: hand-over determination means for measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; message transmission means for generating a request message including the measured qualities and transmitting the generated request message to the base station in the established synchronization when it is determined by the hand-over determination means that the hand-over is necessary; message retransmission means for monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message, and repeating the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and receiving quality update means for re-measuring the receiving qualities of the radio signals transmitted by the base station in the established synchronization and the neighboring base stations, simultaneously with an operation of monitoring the acknowledgement response from the base station, and renewing the measured qualities included in the message to latest values on a basis of a result of the re-measurement.
With this structure, the re-measurement of the receiving quality is executed, simultaneously with the operation of monitoring the acknowledgement response from the base station. For this reason, when the retransmission of the request message is required, the receiving quality measurement values having been obtained at this time can be inserted into the request message and this message can be immediately retransmitted. Therefore, the time required for the retransmission of the request message can be reduced and thereby the hand-over can be smoothly executed.
In according to the other aspect of the present invention, there is provided a CDMA mobile communication terminal apparatus having a function of receiving signals transmitted by a base station in the established synchronization and neighboring base stations, demodulating the received signals, detecting degradation of receiving qualities of the demodulated signals and transmitting a request for hand-over to the base stations in a state of being in the established synchronization with any one of a plurality of base stations. This CDMA mobile communication terminal apparatus is characterized by comprising: hand-over determination means for measuring receiving qualities of the demodulated radio signals and determining necessity of the hand-over on the basis of a result of the measurement; message transmission means for generating a request message including the measured qualities and transmitting the generated request message to the synchronized base station when it is determined by the hand-over determination means that the hand-over is necessary; message retransmission means for monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message, and repeating the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and receiving quality update means for renewing the measured qualities included in the message to latest values before the message retransmission means retransmits the request message.
In according to the other aspect of the present invention, there is provided a control device used in a mobile communication terminal apparatus having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to abase station in a state of being in the established synchronization with any one of a plurality of base stations. The control device is characterized by comprising: hand-over determination means for measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; instruction means for generating a request message including the measured qualities and instructing to transmit the generated request message to the synchronized base station when it is determined by the hand-over determination means that the hand-over is necessary; re-instruction means for monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message and instructing to repeat the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and quality update means for renewing the measured qualities included in the message to latest values when the re-instruction means makes an instruction to retransmit the request message.
Therefore, this invention can provide a control device that can allow the receiving quality measurement values inserted into the message to be always updated to the latest values when the request message is retransmitted. The control device can be implemented by an integrated circuit such as a gate array and the like or a microprocessor comprising a memory.
In according to the other aspect of the present invention, there is provided a hand-over controlling method used in a control device used in a mobile communication terminal apparatus having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to abase station in a state of being in the established synchronization with any one of a plurality of base stations. The hand-over controlling method is characterized by comprising the steps of: measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; generating a request message including the measured qualities and instructing to transmit the generated request message to the synchronized base station when it is determined at the hand-over determination step that the hand-over is necessary; monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message and instructing to repeat the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and renewing the measured qualities included in the message to latest values when the repeating instruction step makes an instruction to retransmit the request message.
Therefore, this invention can provide a hand-over controlling method that can allow the receiving quality measurement values inserted into the message to be always updated to the latest values when the request message is retransmitted.
In according to the other aspect of the present invention, there is provided a storage medium for storing a program to allow a processor to execute a hand-over controlling method used in a mobile communication terminal apparatus (MS) having a function of detecting degradation of receiving quality thereof and transmitting a request for hand-over to abase station in a state of being in the established synchronization with any one of a plurality of base stations. The hand-over controlling method stored in the storage medium is characterized by comprising the steps of: measuring receiving qualities of radio signals transmitted by the base station in the established synchronization and neighboring base stations and determining necessity of the hand-over on the basis of a result of the measurement; generating a request message including the measured qualities and instructing to transmit the generated request message to the synchronized base station when it is determined at the hand-over determination step that the hand-over is necessary; monitoring an acknowledgement response from the synchronized base station in response to the transmitted request message and instructing to repeat the transmission of the request message when there is no response from the synchronized base station within a predetermined time; and renewing the measured qualities included in the message to latest values when the repeating instruction step makes an instruction to retransmit the request message.
Therefore, this invention can provide a storage medium for storing a program to allow a processor to execute the hand-over controlling method that can allow the receiving quality measurement values inserted into the message to be always updated to the latest values when the request message is retransmitted. As for this storage medium, a memory such as a ROM including the EEPROM or a RAM and the like, a floppy disk, a hard disk, an optical disk such as a CD-ROM disk and a DVD disk, a memory card, and the other storage medium that can store the program can be used.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.